1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery for use in the fields of portable devices such as cell-phones and personal computers, power tools such as electric tools and vacuum cleaners, power-driven devices such as electric cars, electric industrial vehicles, electric bikes, electric-assisted bicycles, electric wheelchairs, and electric robots, system power supplies such as load leveling, peak shift, and backup, and others, and more particularly, to improvement in the performance thereof.
2. Description of the Related Art
A power supply unit having high power and high capacity is required in the fields of power tools such as electric tools, and power-driven devices such as electric bikes and electric-assisted bicycles, as compared to the field of portable devices such as cell-phones and personal computers, because fluctuation in the load to a power source is large and a long-term continuous operation is required in the fields of power tools and power-driven devices.
Generally, high-capacity and high-power are incompatible performances in a battery, and it is difficult to simultaneously satisfy both of the performances. For instance, a non-aqueous electrolyte battery such as a lithium ion secondary battery, as an example of high-capacity secondary batteries, is primarily used as a power supply unit in the field of e.g. portable devices, because it allows for a long-term continuous discharge at a low load of about 0.2 C. The non-aqueous electrolyte battery, however, has a current density per electrode area as low as about 0.01 A/cm2 at such a low load operation. Accordingly, the high-capacity non-aqueous electrolyte battery is not suitable as a high-load power supply unit to be used in the field of e.g. power-driven devices such as electric bikes and electric-assisted bicycles, which require discharge with a large current of 0.1 A/cm2 or more in current density. Also, securing pulse discharge characteristics at a large current is important in the field of power-driven devices, because the power source is frequently turned on and off in the field of power-driven devices. It is, however, difficult to obtain a sufficiently large pulse discharge capacity in the high-capacity non-aqueous electrolyte battery, which is generally used in the field of e.g. portable devices. On the other hand, a high-power power supply unit such as a capacitor allows for a discharge at a large current; however, the capacitance thereof is extremely small, which hinders performing a long-term continuous discharge.
As mentioned above, it is difficult to produce a power supply unit that simultaneously satisfies the requirements on both of the characteristics with use of a single kind of battery. In view of the above, a hybrid power supply unit incorporated with a long-term, low-power energy supply unit, and a short-term, high-power power supply unit has been proposed and studied for practical use. For instance, Japanese Unexamined Patent Publication No. Hei 8-308103 (D1), Japanese Unexamined Patent Publication No. 2004-48913 (D2), PCT Unexamined Patent Publication No. WO2002-025761 (D3), and Japanese Unexamined Patent Publication No. 2004-56995 (D4) propose hybrid power supply units, wherein a secondary battery such as a lead battery, a Ni—Cd battery, a nickel metal hydride battery or a lithium ion battery, or a fuel battery is used as a long-term, low-power energy supply unit, and a capacitor (condenser) is used as a short-term, high-power power supply unit.
D1 discloses a hybrid power supply unit provided with a battery, a large-capacitance condenser, and a current controlling circuit. According to the publication, the use efficiency of the battery is improved by the current controlling circuit in such a manner that the battery discharge current to be supplied to the load at a high load current is approximated to the sum of the battery discharge current to be supplied to the load at a low load current and the battery charge current flowing to the condenser. D2 proposes a power supply system for efficiently charging a secondary battery, in which a main battery unit and an auxiliary power supply unit are connected in parallel, and the auxiliary power supply unit and a voltage raising means are connected in series. D3 proposes a hybrid power supply unit provided with a fuel battery and a secondary battery constituted of a multitude of unit secondary cells connected in series, as well as a means for detecting a residual capacity of the unit secondary cells, and a charge controlling means. D4 proposes a hybrid power supply unit including an electric double-layer capacitor provided with a pair of capacitor terminals, an energy storage device, and first and second bidirectional DC/DC converters.
However, the conventional hybrid power supply units as proposed in D1 through D4 employ combination of different kinds of power supply units or different kinds of parts, which requires a complex control system incorporated with a current controlling circuit, a voltage raising means, a residual capacity detecting means, a charge controlling means, and bidirectional DC/DC converters to optimally drive these different kinds of power supply units or the different kinds of parts.